Ferro-aluminum-zirconium alloys



Patented Jan. 10, 1939 UNITED, STATES PATENT OFFICE FERRO-ALUDIINUIW- ZIRCONIUM ALLOYS No Drawing. Application August 29, 1936, Serial No. 98,581

4' Claims.

My invention relates to a new type of a ferrozirconium alloy, and more particularly to a new and improved ferro aluminum-zirconium alloy for use in treating molten steel for the purpose of deoxidizing the molten metal as well as assisting in the removal of gaseous and other objectionable impurities. My improved ferro-aluminum-zirconium alloy also aids in producing a desirably fine grain-size on the steel in which it has been incorporated.

Aluminum and zirconium are well-known in their action as extremely powerful deoxidizers when added to molten steel, and by virtue of this fact and the infusibility of their oxides, they are also effective in conferring an inherently fine grain-size on the steel to which they are added.

This eiiect on grain-size is held to be accounted ior by the presence of extremely fine inclusions within the steel of the oxide or nitride of aluminum or zirconium, or both, on the theory that such fine inclusions retard the normal growth of the crystals when the steel is heated in the ordinary processes of fabrication.

The presence of silicon with these grain-reflning deoxidizers is generally not desirable, since the inclusions resulting from the deoxidation of the steel then take the form of complex silicates which occur in larger particles that do not interfere with normal grain growth when the steel is heated.

The presence of carbon in the zirconium alloy is also objectionable, since it retards the solution of the alloy and its deoxidizing action. The

' ferro-zirconium alloys previously known have always contained over 10% of silicon resulting from the silica in the zirconium ores used, and have been made either by reduction with carbon in an electric furnace, or by a thermit reaction using aluminum powder.

When made by carbon reduction, a high silicon content in the product is imperative in order to prevent the absorption of carbon by the alloy; and thermit reactions are not very suitable for making zirconium alloys on account of the large quantity of expensive aluminum powder which must be consumed to produce sufilcient energy for the reduction. I have now discovered that a new and improved ferro-aluminum-zirconium alloy of low carbon and silicon contents may be made from zircon, a zirconium silicate ore, by first removing the silica therefrom by the methods described in the two U. S. patents to Kinzie No. 1,351,091 of August 31, 1920 and No. 1,588,476 of June 15, 1926, and then reducing the crude zirconium oxide thus obtained, together with iron ore, in a bath of aluminum superheated in an electric furnace.

The final result of these operations is a brittle, silvery alloy which may be readily tapped from the furnace and then separated from the slag. Samples taken from numerous melts of my new ferro-aluminum-zirconium alloy have shown compositions within the following range:

v Per cent Zirconium 25.5 to 37.7 Aluminum 20.81 to 26.52 Iron 31.08 to 50.40 Silicon 2.12 to 6.68 Carbon 0.05 to 0.15

The preferred composition for this low silicon and low carbon fei'ro-alurninum-zirconium alloy for deoxidizing' steel is approximately as follows:

Per cent Zirconium i 35. Aluminum 24. Silicon not more than 5. Carbon 0.1 Iron Balance Lbs. Crude ZrO2 as described above"--. 75 Fine iron ore containing 64.6% iron, and

4.32% silica, with normal impurities; 35 Sodium chlorate 5 Cryolite (sodium aluminum fluoride) 5 The arc was then started between the electrodes in the charge, using volts and 3000 amperes, and after 5 minutes a vigorous reaction occurred. Ten minutes later an addition of 2 lbs.

of zirconia and 2 lbs. of cryolite was made, and

this addition was repeated every ten minutes until the furnace was tapped forty minutes after the reaction. 1

After separating the slag from the cold ingot,

forty-one pounds of alloy were recovered containing approximately:-

Percent Zirconium 36.42 Aluminum I 24.80 Iron- 33.87

Silicon 4.91

Changes may, of course, be made in the amounts of fluxes used, as may seem advisable from the conditions of the furnace and slag, and it is not necessary to add ZrOz after the reaction. For example, with a mix containing 70 lbs. crude ZrOa, 40 lbs. iron ore, 10 lbs. sodium chlorate and -10 lbs. cryolite (milled together), and making only one subsequent addition of 3 lbs. of cryolite, 46 lbs.-. of alloy were obtained containing approximately:--

Per cent Zirconium 35.60 Aluminum 26.42 Iron 32.96 Silicon 5.02

melts of this alloy showed the following average composition after careful sampling and an- I claimas my invention:

1. A ferro-aluminum-zirconium alloy soluble in molten steel and producing fine grain size therein, said alloy consisting of from about 25% to 38% zirconium, aluminum in such amount that the proportion of zirconium to zirconium plus aluminum is between 49 and 64%, 32 to 50% iron,

0.10 to 10% silicon, and carbon not over 0.50%.

2. A ferro-aluminum-zirconium alloy soluble in molten steel and producing fine grain size therein, said alloy consisting of from about 25% to 38% zirconium, aluminum in such amount that the proportion of zirconium to zirconium plus aluminum is between 49 and 64%, 32 to 50% iron, 2 to 7% silicon and from 0.05 to 0.15% carbon.

3. A ferro-alumlnum-zirconium alloy soluble in molten steel and producing fine grain size therein, said alloy consisting of approximately 35% zirconium, 24% aluminum, silicon, 0.1% carbon, and the balance substantially iron.

4. A low-carbon ferro-alloy soluble in molten steel and producing fine grain size therein, said alloy consisting of about 36% zirconium, 25% aluminum, 2 to 7% silicon, from 0.05 to 0.15% carbon, with the balance substantially iron.

GEORGE F. coMs'rocK. 

